Fluorescent pteridine-based nucleoside analogs that can be site-specifically incorporated into DNA oligonucleotides through a phosphodiester linkage have been developed and patented. The fluorescence properties of a series of these compounds have been characterized and potential applications are being investigated. These new fluorophores are promising probes for the study of protein/DNA interactions, because they are not attached to DNA externally and they do not appear to disrupt the tertiary structure of DNA. The utility of these fluorophores as hybridization probes has been patented and is under investigation, and current collaborative studies include development of an assay for tetrad formation and single molecule studies of oligonucleotide/protein interactions using two photon detection. The probes have been licensed by Fidelity Systems, Inc. and are commercially available.